With a recent increase in transmission data, the speed and capacity of the transmission signal are ever on the increase. At the same time, optical transmission apparatuses are required to be equipped with switch fabrics having large-capacity TSI (Time Slot Interchange, or cross connect) functions.
Also, optical transmission apparatuses adapted for SONET (Synchronous Optical Network) or SDH (Synchronous Digital Hierarchy) use ring networks such as SONET rings to secure network reliability.
Ring network systems include UPSR (Unidirectional Path Switched Ring) and BLSR (Bidirectional Line Switched Ring) systems. Through such ring network systems, different optical transmission apparatuses on ring networks are relieved from a fault which may occur by a protection configuration using a redundant channel.
When such optical transmission apparatuses on ring networks set lines for digital multiplex transmission data, the time slots for the digital multiplex transmission data are allotted and thus channel positions for the digital multiplex transmission data are replaced.
Japanese Laid-open Patent Publication No. 2001-237794 discloses a technique in which upon occurrence of a fault in the traffic of the operation system, the traffic of the operation system can be switched independently of the traffic setting of the spare system or the activation of other APS (Automatic Protection Switch).
The above-mentioned conventional technique poses such problems, however, that the processing capacity required for line setting is remarkably increased when a measure is taken against a fault or various lines for the transmission data are set for the optical transmission apparatus making up the ring network, and the line setting process is required be to executed at a high speed, resulting in an increased size of the circuits to be included in the optical transmission apparatus.